Spent lubricating oils are lubricants discarded after use from engines such as automobiles, ships and industrial applications such as mining, hydraulic engines. New lubricants contain base stock and additives for enhancing the performance of the base stock in an engine. Base stocks are generally oils of the vacuum gasoil boiling range from paraffinic or naphthenic petroleum crude oils. Alternately, the base stock could be synthetically produced such as polyalfaolefins. The additives are typically organ metallic compounds containing Mg, Ca, Zn, P, S, and Si with molecular weights in few 100 s to a few 1000 s.
Commercial recycling of spent lubrication oil involves of varying degrees of processing, starting with simple filtration of solids to evaporation of water to more elaborate processing that involves separation of base stock (vacuum gasoil like hydrocarbons) from everything else that is present in spent lubricants. Distillation—use of heat and pressure (vacuum)—is the dominant commercial method of recovering base stock (vacuum gasoil) from spent lubricants.
Generally, separation by distillation/evaporation of water, light hydrocarbons, solvents, coolants, fuel, and lubricating oil base stock (LOBS) from spent lubricating oil is achieved in multiple steps.
The distillation of water, light hydrocarbons, fuel, and solvents is carried out in conventional apparatus. This conventional apparatus is either a shell and tube heat exchanger or a furnace (fired heater) for heating the spent oil to the distillation temperature.
Commercially, the separation or recovery of LOBS from discarded lubricants is predominantly carried out by use of a wiped-film (WFE) or a thin-film evaporator with an agitating rotor (ATFE) in one or two steps (in series). These TFE or WFE equipment, are described in detail, as are their principles of operation and typical operating conditions, in “Recent Technology Development in Evaporative Recycling of Discarded Oil” by J. Bishop and D. Arlidge and in “Thin-film Distillation as a Tool in Recycling of Discarded Oil” by J. F. Pauley, both articles appearing in Third International Conference on Discarded Oil Recovery and Reuse, 1978. See also U.S. Pat. No. 4,073,719, U.S. Pat. No. 3,348,600 and U.S. Pat. No. 4,160,692 incorporated herein by reference.
In comparison to standard shell and tube heat exchangers, the WFE and ATFE are expensive to purchase and install, more complicated to operate and maintain (clean, repair). There is also a size limitation (<50 m2 heat transfer area) and units larger than 10 m2 area are bulky. It would be advantageous to either eliminate or reduce the scope and size of WFE/ATFE distillation in processing of spent lubricating oil.